Effects of human presence on the long-term trends of migrant and resident shorebirds: evidence of local population declines

Animal migration in the Anthropocene: threats and mitigation options

Animal migration has fascinated scientists and the public alike for centuries, yet migratory animals are facing diverse threats that could lead to their demise. The Anthropocene is characterised by the reality that humans are the dominant force on Earth, having manifold negative effects on biodiversity and ecosystem function. Considerable research focus has been given to assessing anthropogenic impacts on the numerical abundance of species/populations, whereas relatively less attention has been devoted to animal migration. However, there are clear linkages, for example, where human-driven impacts on migration behaviour can lead to population/species declines or even extinction. Here, we explore anthropogenic threats to migratory animals (in all domains - aquatic, terrestrial, and aerial) using International Union for the Conservation of Nature (IUCN) Threat Taxonomy classifications. We reveal the diverse threats (e.g. human development, disease, invasive species, climate change, exploitation, pollution) that impact migratory wildlife in varied ways spanning taxa, life stages and type of impact (e.g. from direct mortality to changes in behaviour, health, and physiology). Notably, these threats often interact in complex and unpredictable ways to the detriment of wildlife, further complicating management. Fortunately, we are beginning to identify strategies for conserving and managing migratory animals in the Anthropocene. We provide a set of strategies that, if embraced, have the potential to ensure that migratory animals, and the important ecological functions sustained by migration, persist.

Frequency-dependent tolerance to aircraft disturbance drastically alters predicted impact on shorebirds

Anthropogenic disturbance of wildlife is increasing globally. Generalizing impacts of disturbance to novel situations is challenging, as the tolerance of animals to human activities varies with disturbance frequency (e.g. due to habituation). Few studies have quantified frequency-dependent tolerance, let alone determined how it affects predictions of disturbance impacts when these are extrapolated over large areas. In a comparative study across a gradient of air traffic intensities, we show that birds nearly always fled (80%) if aircraft were rare, while birds rarely responded (7%) if traffic was frequent. When extrapolating site-specific responses to an entire region, accounting for frequency-dependent tolerance dramatically alters the predicted costs of disturbance: the disturbance map homogenizes with fewer hotspots. Quantifying frequency-dependent tolerance has proven challenging, but we propose that (i) ignoring it causes extrapolations of disturbance impacts from single sites to be unreliable, and (ii) it can reconcile published idiosyncratic species- or source-specific disturbance responses.

Some metals and metalloids in the blood of three species of shorebirds increase while foraging during two-week migratory stopover in Delaware Bay, New Jersey

Most migratory shorebird species are declining, some are endangered, and some may be vulnerable to contaminants on long distance travel between wintering grounds and high latitude breeding grounds. We examined whether shorebirds accumulated trace elements at the Delaware Bay (New Jersey) stopover by testing the null hypothesis that there was no difference in the levels of arsenic, cadmium, chromium, lead, mercury, and selenium in blood of three species of shorebirds collected early in their stopover compared to levels in blood collected about two weeks later near the end of the stopover, before departing for breeding grounds. There were significantly higher levels of all metals and metalloids in the blood of ruddy turnstone (Arenaria interpres) later in May than earlier. There were seasonal increases in blood levels of arsenic and selenium for all three species. Chromium and lead levels also increased in red knots (Calidris canutus). These increases occurred although the birds were only present for about two weeks. Levels of arsenic, mercury, and lead in knots and selenium in sanderlings (Calidrris alba), exceeded reported effects levels. These results have potential implications for studying the refueling physiology, energetics, and feeding behavior of migratory shorebirds. However, they also suggest cause for concern because the increased contaminant loads occur in a short period, and the high metal level bolus received all in a few days may result in adverse effects.

The influence of tourist visitation on the heterophyl to lymphocyte ratios and trophic values of Magellanic penguins (Spheniscus magellanicus) at Martillo Island, Argentina

Wildlife tourism is increasing worldwide and monitoring the impact of tourism on wild populations is of the utmost importance for species conservation. The Magellanic penguin Spheniscus magellanicus colony at Martillo Island, Argentina, was studied in the 2016-2020 breeding seasons. In all seasons, adults and chicks belonged to: (i) an area close to or within the tourist trail or (ii) an area far from the tourist trail and out of sight of the tourists. Blood samples were taken for carbon and nitrogen stable isotope composition, in order to estimate trophic niches, and for smears that were made in situ and were then stained in the laboratory where leucocyte counts and differentiation were made under optical microscope. Heterophil to lymphocyte ratios were used as proxies of stress. Repeated sampling showed individual stress levels reduced while wintering. In 2017, stress levels and trophic values were lower than 2018 for the same individuals. Trophic levels did not differ between tourism and no tourism areas within each season, and differed between 2017 and the remaining seasons, indicating a possible diet shift that year. Stress levels were higher for the tourism area than the no tourism area for adults and chicks in all years except for 2020, when stress levels in the tourism area were lower and similar to the no tourism area that year and previous years. Vessel transit within the Beagle Channel and tourist visitation to the penguin colony was greatly reduced in 2020 due to the Covid-19 pandemic. A combination of internal characteristics and external factors may be affecting the stress physiology of individuals. Therefore, future research should include sampling of multiple aspects of penguin physiology, behaviour and environmental context in order to evaluate each effect on Magellanic penguin stress and, ultimately, inform the conservation of this iconic species in time.

Illegal and Exploitative Sand-Digging Activities Could Be Managed to Create Suitable Nesting Habitats for Blue-Tailed Bee-Eaters (Merops philippinus)

The development of human society often interferes with wild animals and their natural habitats. Interference during resource exploitation is mostly negative; however, in some cases, it can be positive and even have significance for some species. In this study, we investigated the number of blue-tailed bee-eaters (Merops philippinus), a species under 'state protection category II' in China, between controlled and manipulated nesting habitats from 2017 to 2022. Our results indicated that commercial sand-digging activities, either illegal or approved, initially created suitable nesting habitats to attract blue-tailed bee-eaters but subsequently led to damage of nests or nesting habitats. However, sand digging can be modified by avoiding the breeding season to provide safe and suitable nesting habitats for bee-eaters. The number of breeding birds more than tripled when digging during the breeding season was avoided. We also found that conventional conservation strategies, which strictly prohibited sand-digging activities, did not contribute to the nesting habitats of bee-eaters. This study enriches the theories of conservation biology and emphasizes the importance of dialectical thinking regarding exploitative and seemingly destructive activities.

Spatio-Temporal Distribution Patterns and Determinant Factors of Wintering Hooded Cranes (Grus monacha) Population

Hooded Cranes (Grus monacha) rely on wetlands for the majority of their life cycle and respond to the environmental conditions during the wintering period. Future conservation planning should be driven by an understanding of how cranes respond to environmental factors at degraded wetland sites and the changes in their spatio-temporal distribution. In recent years, the spatial and temporal distribution of waterbirds and determinant factors have become a research focus. However, research on the specific factors influencing the relative abundance of Hooded Cranes from multiple perspectives in the different habitat patches at Shengjin and Caizi Lakes is lacking. Therefore, from 2021 to 2022, we investigated the quantity and distribution of Hooded Cranes in the upper part of Shengjin and Baitu Lake part of Caizi Lakes. We considered multiple habitat variables, including patch size, food biomass, food availability, and human disturbance, and analyzed the dynamic changes in the distribution of the population in different wintering periods. We used model selection and averaging to select the best model and identify key variables. During different wintering periods, the spatio-temporal distribution of the crane population differed in the upper part of Shengjin Lake, but the crane was mainly distributed in the northern part of the Baitu Lake part of Caizi Lake. The model that included food biomass and patch size was the best for predicting the relative abundance of Hooded Cranes. Cranes foraged in areas with large patches and abundant food resources. Therefore, we suggest reserving patch integrity and availability in the current habitats and protecting and restoring the main food resources to provide high-quality habitat patches and plentiful food resources for wintering populations of Hooded Cranes.

Ecocultural attributes are important components of perceptions of the importance of coastal beaches of conservation concern

Sandy beaches along coasts and bays are prime real estate for houses and condominiums, marinas, recreation, and tourism for people living in urban and suburban areas within a hundred km of coasts. Human encroachment and disturbance can be a determinant of success of animals in human-impacted systems, particularly shorebirds. Understanding perceptions of people visiting critical habitats can aid in conservation of shorebirds and associated ecosystems, as well as improving the human experience. This paper examines valuation of ecological resources and ecocultural attributes of visitors to 9 beaches on the New Jersey shore of Delaware Bay during a shorebird migratory stopover period. Ecocultural attributes are those cultural activities or experiences that require an intact ecosystem to be optimal, including activities of recreational, aesthetic or spiritual importance. Using a Likert scale, interviewees (N = 279) rated the importance of shorebirds and/or horseshoe crabs Limulus polyphemus, ambiance, existence, aesthetics, the beach itself, and recreational activities (photography, birding, and fishing) to the Bay and to their experience. Although shorebirds/crabs were rated as most important (mean rating well over 4.0 out of 5); ecocultural attributes (ambience, existence, aesthetics, the beach itself) were rated higher (rating well over 3) than recreation, hardcore or casual birding, photography (mean rating around 3) and fishing (rating less than 2). Although some ratings of these resources and attributes were positively correlated, many values for birds and/or crabs were not correlated with the ecocultural attributes. Women rated most resources and ecocultural attributes higher than did men, and older people rated them higher than younger interviewees. It was unexpected that the ecocultural attributes played so heavily in the attractiveness of the beach. The importance and implication of these findings are discussed for management and conservation of these beaches, including the importance of ecocultural resources within a context of local community involvement.

Effects of COVID-19 lockdowns on shorebird assemblages in an urban South African sandy beach ecosystem

Human pressures are pervasive in coastal ecosystems, but their effect magnitudes are masked by methodological limitations. Government lockdowns associated with the global COVID-19 pandemic can address this gap since lockdowns are effectively manipulations of human presence in ecosystems at scales unachievable otherwise. We illustrate this using a study on shorebirds in an urban South African sandy beach ecosystem. Data collected prior to (2019) and during the COVID-19 (2020) pandemic indicated an inverse relationship between shorebird and human numbers, but this was stronger in 2020. In 2020, human exclusion resulted in a six-fold increase in shorebird abundance relative to 2019. Following easing of lockdowns, shorebird abundance declined by 79.6% with a 34.1% increase in human density. Our findings highlight the sensitivity of shorebirds to recreational disturbance, the potential for current methodological approaches to underestimate repercussions of disturbance and the capacity for COVID-19 lockdowns to refine understanding of human-induced stress in ecosystems.

Nestedness theory suggests wetland fragments with large areas and macrophyte diversity benefit waterbirds

Many artificial wetland constructions are currently underway worldwide to compensate for the degradation of natural wetland systems. Researchers face the responsibility of proposing wetland management and species protection strategies to ensure that constructed wetlands positively impact waterbird diversity. Nestedness is a commonly occurring pattern for biotas in fragmented habitats with important implications for conservation; however, only a few studies have focused on seasonal waterbird communities in current artificial wetlands. In this study, we used the nestedness theory for analyzing the annual and seasonal community structures of waterbirds in artificial wetlands at Lake Dianchi (China) to suggest artificial wetland management and waterbird conservation strategies. We carried out three waterbird surveys per month for one year to observe the annual, spring, summer, autumn, and winter waterbird assemblages in 27 lakeside artificial wetland fragments. We used the NeD program to quantify nestedness patterns of waterbirds at the annual and seasonal levels. We also determined Spearman partial correlations to examine the associations of nestedness rank and habitat variables to explore the factors underlying nestedness patterns. We found that annual and all four seasonal waterbird compositions were nested, and selective extinction and habitat nestedness were the main factors governing nestedness. Further, selective colonization was the key driver of nestedness in autumn and winter waterbirds. We suggest that the area of wetland fragments should be as large as possible and that habitat heterogeneity should be maximized to fulfill the conservation needs of different seasonal waterbirds. Furthermore, we suggest that future studies should focus on the least area criterion and that vegetation management of artificial wetland construction should be based on the notion of sustainable development for humans and wildlife.

Defining Human Disturbance to Shorebirds Using Manager and Scientist Input

Shorebird researchers and land managers recognize human disturbance as a serious threat facing shorebirds. Yet, a common understanding of what defines human disturbance is lacking. To address this issue, we employed the Delphi technique, an iterative consensus-building social science method, to bring scientists and managers together to develop a shared definition of human disturbance and a list of priority human activities that could affect migratory shorebirds. During four iterative rounds, participants with extensive knowledge on human disturbance to shorebirds from varying geographic locations within the Northeastern U.S. worked together to produce a shared understanding. Through analyzing participants' open-ended responses, we identified important themes for the definition. The participants then refined and ranked these themes through surveys, and the top-ranked themes were used to draft a final definition also reviewed by the participants. Participants provided 94 human activities in response to our request to list and describe all potential human disturbances that affect shorebirds during fall migration. From there, we grouped the activities into 23 categories. Through rating and ranking tasks, participants reduced this list to 12 priority disturbance categories that represent the perceived most significant human disturbances in the Northeastern United States. We also compared responses among the different participant groups (i.e., managers, scientists, and manager/scientists), finding that groups' responses generally did not significantly differ. While nearly all participants were satisfied with the process, we provide some suggestions to improve it. The outputs of the Delphi technique have informed a best practices guidance document for shorebird management.

Quantifying human presence in a heterogeneous urban landscape

Humans are a keystone species in urban ecosystems. Although the impact of human activities is increasingly reported in behavioral and evolutionary ecology, little is known about the effects of physical human presence per se. Of particular relevance is the extent to which human presence (sometimes referred to as human disturbance), is repeatable across the urban mosaic over time. We quantified human presence at fixed locations—here in a 15-m radius of great tit nestboxes—within six urban and suburban study sites. While overall human presence did not differ between urban sites, it was significantly higher than in the suburban village. Moreover, considerable variance between fixed locations was observed within each site. We reported overall high repeatability of human presence for all sites (0.57 < R < 0.88, mean: 0.76, median: 0.77). We further simulated datasets of human presence made of an increasing number of counts, and demonstrated that 10 counts of human presence (each 30 s long) made at each fixed location can generate a highly reliable indicator of human presence (R ≥ 0.6) for any urban site. We thus confirm that human presence is repeatable across the urban mosaic, thereby offering consistent cues to urban wildlife of human presence or absence in space and time. Importantly, our approach of human presence quantification allows for an effort-efficient approach to understand the effects of physical human presence at designated temporal timeframes, thereby allowing to reliably test the effects of human presence on the behavior and ecology of urban wildlife.

Effects of ecological and anthropogenic factors on waterbird abundance at a Ramsar Site in the Yangtze River Floodplain

Continuing declines in abundance of many waterbird species on wetland ecosystems require explanations to support effective management interventions. We used 6 year survey data from Shengjin Lake National Nature Reserve in the Yangtze River Floodplain, China, to study the effects of ecological and anthropogenic variables as determinants of waterbird species abundance. Our results showed that effects were guild-dependent, although distance to nearest human settlements had the largest adverse effects on bird abundance across all guilds. These results suggested that although the abundance of waterbird species could be affected by habitat conditions and buffalo grazing activities, Yangtze River Wetlands would most likely benefit most from reduced pressure from the proximity to the surrounding human population. We suggest that screening and/or restricting public access at some key sites may be the most cost-efficient way to restrict or reduce human activity in these wetlands, to improve the conservation status and wintering conditions for these waterbirds.

Mapping wader biodiversity along the East Asian-Australasian flyway

Background and goal

The study is conducted to facilitate conservation of migratory wader species along the East Asian-Australasian Flyway, particularly to 1) Identify hotspots of wader species richness along the flyway and effectively map how these might change between breeding, non-breeding and migratory phases; 2) Determine if the existing network of protected areas (PA) is sufficient to effectively conserve wader biodiversity hotspots along the EAAF; 3) Assess how species distribution models can provide complementary distribution estimates to existing BirdLife range maps.

Methods

We use a species distribution modelling (SDM) approach (MaxEnt) to develop temporally explicit individual range maps of 57 migratory wader species across their annual cycle, including breeding, non-breeding and migratory phases, which in turn provide the first biodiversity hotspot map of migratory waders along the EAAF for each of these phases. We assess the protected area coverage during each migration period, and analyse the dominant environmental drivers of distributions for each period. Additionally, we compare model hotspots to those existing range maps of the same species obtained from the BirdLife Internationals’ database.

Results

Our model results indicate an overall higher and a spatially different species richness pattern compared to that derived from a wader biodiversity hotspot map based on BirdLife range maps. Field observation records from the eBird database for our 57 study species confirm many of the hotspots revealed by model outputs (especially within the Yellow Sea coastal region), suggesting that current richness of the EAAF may have been underestimated and certain hotspots overlooked. Less than 10% of the terrestrial zones area (inland and coastal) which support waders are protected and, only 5% of areas with the highest 10% species richness is protected.

Main conclusions

The study results suggest the need for new areas for migratory wader research and conservation priorities including Yellow Sea region and Russian far-East. It also suggests a need to increase the coverage and percentage of current PA network to achieve Aichi Target 11 for Flyway countries, including giving stronger consideration to the temporal dynamics of wader migration.

Habitat risk: Use of intertidal flats by foraging red knots (Calidris canutus rufa), ruddy turnstones, (Arenaria interpres), semipalmated sandpipers (Calidris pusilla), and sanderling (Calidris alba) on Delaware Bay beaches

Shorebirds usually forage on intertidal flats that are exposed during low tide, and roost on higher areas when the tidal flats are covered with water. During spring migration on Delaware Bay (New Jersey) shorebirds mainly forage on horseshoe crab (Limulus polyphemus) eggs that are concentrated at the high tide line. However, they also use other habitats for foraging. We examined habitat use of 4 species of shorebirds (with declining populations) at five Delaware Bay beaches to determine their use of the intertidal habitat (2015, 2016). We observed birds in three sections at different distances from the mean high tideline (< 100 m, 101-200 m, and 201-300 m)ne. We examined the presence of red knots (Calidris canutus rufa), ruddy turnstones (Arenaria interpres), semipalmated sandpipers (Calidris pusilla), and sanderling (Calidris alba) as a function of date, tide cycle, section shorebirds foraged from the mean high tide line, and presence of other shorebird species. Understanding how these species use the intertidal flats is important because these habitats are at risk from coastal development, sea level rise, and decreases in intertidal space, including the possible expansion of intertidal oyster culture. Overall, knots were present in the intertidal on 67% of the surveys, turnstones were present on 86% of the surveys, semipalmated sandpipers were present on 77% of the surveys, and sanderling were present on 86% of the surveys. Use of the intertidal flats varied among beaches. Peak and mean numbers of shorebirds/ decreased in each census section, as distance to mean high tideline increased. In general, shorebirds foraged at the waters' edge during high tide, and then moved out onto the intertidal flats. The strongest interspecific associations were between red knots and ruddy turnstones, and the lowest associations were between sanderling and semipalmated sandpipers. Variations in numbers of each species in 2016 were mainly explained by the number of other species, section (distance from the mean high tide line), location (one of 5 beaches), and date for all species (and minutes to low tide for sanderling). These data indicate that these 4 species use intertidal flats as they become available, and that the mean number in each newly exposed census section of the flats may be lower than in the previous one, partly as a result of some birds remaining in each previously-exposed section. We discuss the management and regulatory implications of shorebird use of the intertidal flats, which include protection of high quality intertidal for foraging by shorebirds.

Use of intertidal habitat by four species of shorebirds in an experimental array of oyster racks, reefs and controls on Delaware Bay, New Jersey: Avoidance of oyster racks

Many shorebirds breed in Arctic habitats, and migrate south to wintering quarters in the Southern Hemisphere. Shorebirds mainly forage on intertidal mudflats at low tide. A key spring stopover for shorebirds in North America is Delaware Bay, New Jersey, where shorebirds feed on horseshoe crab (Limulus polyphemus) eggs at high tide. The importance of intertidal to migrant shorebirds has been overlooked. This paper examines foraging of 4 shorebird species at Reeds Beach, Delaware Bay. The intertidal zone was divided into an experimental array with oyster racks, artificial reefs, and controls to quantify the number of birds present in each section. The best models for all species (except sanderling, Calidris alba) explained over 60% of variation in number present as a function of other shorebirds, date, and treatment. Time of day was the only factor affecting the number of sanderlings. Date is a contributing factor because numbers are low in early May, peak by May 20-25th, and decrease in late May as shorebirds leave for the Arctic. Red knots (Calidris canutus rufa), turnstones (Arenaria interpres), and semipalmated sandpipers (Calidris pusilla) were present less often, and in smaller numbers in the oyster rack treatment (compared to the other treatments). There was a high association between foraging species. The data clearly show avoidance of the oyster racks by knots, turnstones and semipalmated sandpipers, but they did not avoid those with reefs or the control. These results are important because of the desire to expand aquaculture along the Delaware Bay into prime shorebird foraging areas. The Precautionary Principle dictates that the expansion of intertidal oyster culture be halted in areas of high foraging value for red knots (threatened in the U.S.) and other shorebirds until any effects on fitness are determined.

Experimental evidence of human recreational disturbance effects on bird-territory establishment

The worldwide increase in human outdoor activities raises concerns for wildlife. Human disturbances, even at low levels, are likely to impact species during sensitive periods of the annual cycle. However, experimental studies during the putative sensitive period of territory establishment of birds which not only investigate low disturbance levels, but which also exclude the effect of habitat modification (e.g. walking trails) are lacking. Here, we experimentally disturbed birds in forest plots by walking through twice a day during territory establishment. Later we compared the breeding bird community of experimentally disturbed plots with that of undisturbed control plots. We discovered that the number of territories (-15.0%) and species richness (-15.2%) in disturbed plots were substantially reduced compared with control plots. Species most affected included those sensitive to human presence (assessed by flight-initiation distances), open-cup nesters and above-ground foragers. Long-distance migrants, however, were unaffected due to their arrival after experimental disturbance took place. These findings highlight how territory establishment is a sensitive period for birds, when even low levels of human recreation may be perceived as threatening, and alter settlement decisions. This can have important implications for the conservation of species, which might go unnoticed when focusing only on already established birds.

Regional drivers of clutch loss reveal important trade-offs for beach-nesting birds

Coastal birds are critical ecosystem constituents on sandy shores, yet are threatened by depressed reproductive success resulting from direct and indirect anthropogenic and natural pressures. Few studies examine clutch fate across the wide range of environments experienced by birds; instead, most focus at the small site scale. We examine survival of model shorebird clutches as an index of true clutch survival at a regional scale (∼200 km), encompassing a variety of geomorphologies, predator communities, and human use regimes in southeast Queensland, Australia. Of the 132 model nests deployed and monitored with cameras, 45 (34%) survived the experimental exposure period. Thirty-five (27%) were lost to flooding, 32 (24%) were depredated, nine (7%) buried by sand, seven (5%) destroyed by people, three (2%) failed by unknown causes, and one (1%) was destroyed by a dog. Clutch fate differed substantially among regions, particularly with respect to losses from flooding and predation. ‘Topographic’ exposure was the main driver of mortality of nests placed close to the drift line near the base of dunes, which were lost to waves (particularly during storms) and to a lesser extent depredation. Predators determined the fate of clutches not lost to waves, with the depredation probability largely influenced by region. Depredation probability declined as nests were backed by higher dunes and were placed closer to vegetation. This study emphasizes the scale at which clutch fate and survival varies within a regional context, the prominence of corvids as egg predators, the significant role of flooding as a source of nest loss, and the multiple trade-offs faced by beach-nesting birds and those that manage them.